Building ARM Toolchain

Originally this was a complete walkthrough the compilation and installation process of the ARM Toolchain. Now there is a script called Summon ARM Toolchain that does everything automatically.
Apart from the standard development tools linux users should install the following extra packages: libgmp3-dev and libmpfr-dev

For Debian/Ubuntu:

> apt-get install libgmp3-dev libmpfr-dev

Or use build-dep to automatically grab everything needed to compile gcc: